1. Field of the Invention
The present invention relates generally to transceiver modules, and more particularly is a transceiver module with an EMI shield that is sealed when the module is inserted into a cage mounted on a PC board.
2. Description of the Prior Art
Computers and related peripheral equipment, and satellite and communication systems, have in the recent past evolved extremely rapidly. These systems require ever increasing data transfer rates to perform the highly complex tasks that drive the systems, such as digital signal processing, image analysis, and communications. With current demands, optical couplers are used to transfer signals over short and long distances between computers, between two circuit boards in one computer, and even between multiple chips on a single printed circuit board. The use of high speed optical signals in place of electrical interconnections increases the achievable data transfer rate.
An optical transmitter/receiver module typically includes both light emitting devices such as vertical cavity surface emitting lasers (VCSELs) and light detecting devices such as photodiodes. Driver/receiver circuitry modules, typically in the form of application specific integrated circuit (ASIC) chips, include driver circuitry which receives electrical signals from one device and drives the VCSELs in response. The ASIC also includes receiver circuitry for receiving signals from the photodiodes and, in response, for processing those signals into an appropriate output. The combination of the VCSELs, the photodiodes, and the ASIC circuitry is commonly referred to as an optical transceiver or a fiber optic transceiver.
To provide heat dissipation means and EMI (electro-magnetic interference) protection for the circuitry of the transceivers, the transceivers are enclosed in packages called modules. The main subject of this invention is the IPF module that includes, per MSA (Multi Source Agreement) standards, an EMI dissipation means at the mouth of the cage receiving the module.
The problem presented by the EMI shield is that the shield must wrap around the rectangular module. This presents four edge areas that are very difficult to cover with a stamped sheet metal EMI shield. The stamping process requires some boundary distance between the fingers and the edge of the base of the shield. With ordinary straight projecting fingers in the shield, an unacceptably large gap is created in the EMI shield at each of its corners.
Accordingly, it is an object of the present invention to provide a means to form an EMI shield at the mouth of the cage receiving a transceiver.
It is another object of the present invention to provide an EMI shield that forms sealed corners when the transceiver is inserted into the cage.